The invention relates to a method for determining the corrosiveness of naphthenic acid contained in crude oils and refinery streams.
The corrosiveness of various components in crude oil and refinery streams is a real problem in that excessively corrosive components in such streams can destroy the distillation units in the refinery and other equipment as well
One widely accepted method for representing the corrosiveness of a crude oil and/or refinery stream is the total acid number (TAN), which is determined as a number of milligrams of KOH per gram of material in question. It has been found, however, that total acid number is not an accurate indicator of corrosiveness of the crude oil and/or refinery stream in question, since acidity is not necessarily correlated directly with corrosiveness.
The conventional method to measure naphthenic acid corrosiveness is by means of placing coupons in the corrosive medium for a given time at the relevant temperature and pressure, according to "tandard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens", G1-90 and "Standard Guide for Corrosion Test in High Temperature or High Pressure Environment, or Both", G111-97, in Volume 03.02; Wear and Erosion; Metal Corrosion, of the 1998 Annual Book of ASTM Standards, Section 3:Metals Test Methods and Analytical Procedure".
An alternative method for measuring naphthenic acid corrosiveness is a weight loss measuring method disclosed in a publication entitled "Naphthenic Acid Corrosion in a Refinery Setting", By Babaian-Kibala E., et al., presented as paper 631 in the NACE International Annual Conference, Houston Tex., 1993.
These weight loss methods measure the corrosion as a total event and they are not capable of distinguishing between the corrosion processes caused by sulfur and naphthenic acids. Since the corrosion product of the naphthenic acid attack is soluble, Babaian-Kibala E., et al., measured the weight of the corrosion film on a steel coupon in units of mg/cm.sup.2, which is the weight of corrosion product, and the total weight loss in mils per year, which is the corrosion rate. From this data they calculated a ratio of corrosion rate to corrosion product. If this ratio is less than 10, they state that the naphthenic acid contribution is little or non-existent. However, if the ratio exceeds 10, then naphthenic acid is said to have made a significant contribution to the corrosion process. The method does not work well with crude oils because during the test the crude oil tends to form a coke layer together with a corrosion film on the coupon surface. This results in errors when measuring the corrosion film weight.
Considering the foregoing, it is clear that the need remains for a simple, reliable and effective method for measuring the corrosiveness of naphthenic acid contained in a fluid such as crude oils or refinery streams.
It is therefore the primary object of the present invention to provide a method whereby corrosiveness of naphthenic acid can readily be determined.
It is a further object of the present invention to provide such a method wherein required materials are readily available.
It is a still further object of the present invention to provide such a method which can readily be incorporated for measurements carried out in the field, or in laboratories and the like.
Other objects and advantages of the present invention will appear hereinbelow.